Recycling and utilization of the rubber recovered from the waste tires has been the subject of intense study as the accumulation of waste rubber tires is a major environmental problem. U.S. Pat. Pub. No. 20070249762 to Sylvester describes rubber modified asphalt cement compositions in which rubber crumb is de-vulcanized using dodecylbenzene sulfonic acid (DBSA). DBSA also catalyze reactions of the de-vulcanized rubber with molecules present in asphalt. Rubberized concrete is another use for crumb rubber that is recovered from the waste tires. However, when hydrophobic rubber particle is in composite with hydrophilic cement, the mechanical strength of the resulting concrete is reduced significantly. U.S. Pat. No. 5,456,751 to Zandi et al, U.S. Pat. No. 5,762,702 to Guy, and U.S. Pat. Publication No. 20050096412 to Petr et al, conclude that mixing crumb rubber with the cement creates relatively weak physical bonding between the rubber particulates and cement matrix, which results in a significant reduction in the mechanical properties of the rubberized concrete that severely limits its application. Conventional rubberized concrete uses superplasticizers to improve the weak physical bonding between, the hydrophobic rubber particulates and the hydrophilic cement matrix to make the rubberized concrete composite acceptable for selected applications.
To improve the mechanical properties of the rubberized concrete, surface treatment methods have been developed to modify the crumb tire rubber so as to generate stronger physical/chemical bonding or substantially stronger chemical bonding with the surrounding cement matrix. Segre et al. disclose sodium hydroxide treatment to enhance the adhesion of tire rubber particles to the cement paste, but the resulting rubberized concrete still showed a 33% reduction in the compression strength as compared to the conventional concrete. (Segre, N.; Joekes, I., “Use of tire rubber particles as addition to cement paste”, Cement and Concrete Research 2000, 30 (9), 1421-1425). U.S. Pat. No. 5,849,818 to Walles, et al. discloses a method to sulfonate the outer layer of rubber particles by treatment with a reactant gas containing sulfur trioxide. The rubber (polymer) particles are covered with a skin of the sulfonate layer containing a high amount of sulfonic acid or sulfonate moieties. These sulfonated particles are used as articles of manufacture such as aggregates in cements, organic resins, cellulosics, and so forth, with beneficial properties being imparted to the composite. In particular, concrete can be made from Portland cement that incorporates these aggregates.